The formation and maturation of calcium phosphate prepared from physiological-like solutions is being studied with a number of physical-chemical and ultrastructural techniques including standard analytical chemistry procedures, electron microscopy and x-ray diffraction. Topics of present interest include (1) phase changes in aqueous calcium phosphate suspensions prepared by inoculating stable supersaturated solutions with apatite crystals; (2) effect of ionic fluoride and magnesium on the formation, growth, and stability of precursorphases to crystalline apatite.